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Which Skid Steer Attachments Require High Flow?

Most skid steer attachments on the market are designed with standard flow hydraulics. However, when an attachment needs a large amount of hydraulic horsepower, manufacturers will design them to be used with high-flow skid steers.

Here are a few standard skid steer attachments that often require high flow:

  • Drum Mulchers

  • Swing Arm Stump Grinders

  • Severe Duty Cold Planers

Let's dig a bit deeper into this.

What Do We Mean By "High Flow Skid Steer Attachments"

High-flow skid steer attachments are hydraulically powered attachments that require a higher flow of fluid than the typical standard flow attachment. A High flow skid steer attachment needs to be paired with a skid steer with high-flow hydraulics.

High-flow hydraulics is an option that many modern skid steer manufacturers offer. A typical skid steer with high flow will be able to produce 26 to 40+ gallons per minute of flow, but this will vary by brand and model.

Why Do Some Skid Steer Attachments Require High Flow Hydraulics?

Some skid steer attachments have a higher demand for hydraulic horsepower than others. Take, for example, a cold planer milling concrete versus a brush cutter cutting grass. The cold planer is going to need more horsepower than the brush cutter.

This extra horsepower will come from a higher hydraulic flow rate.

A higher hydraulic flow rate increases hydraulic horsepower when pressure remains constant. The formula to represent this is:

Gallons Per Minute (GPM) times Hydraulic pressure in pounds per square inch (PSI) divided by 1,714 equals hydraulic horsepower.

For example, a standard flow skid steer with 17GPM of hydraulic flow at 3,500 PSI will produce around 34HP, while a 40GPM high flow skid steer at the same 3,500 PSI will produce over 80HP of hydraulic power.

Horsepower is the measuring stick for how much "work" is getting done in a set amount of time. When you need an attachment with high horsepower, you increase the hydraulic flow rate to the motor, and that's how you end up with a high-flow attachment!

Here Are Some Popular Attachments That Require High Flow Hydraulics

Blue Diamond's Drum Mulcher

As with most drum mulcher attachments on the market, Blue Diamond's drum mulcher requires your skid steer to have a high-flow hydraulic system that can operate at 35 to 52 Gallons per minute.

The hydraulic motor on the drum mulcher needs to keep the drum spinning at speeds up to 3,600RPM while constantly meeting the resistance of trees and other debris, which demands a lot of horsepower.

If we used this drum mulcher with a high flow Kubota SVL97 at 40GPM and 3500PSI, we would produce approximately 81.6HP, which would be more than sufficient to run the mulcher.

When we look a bit closer at the drum mulcher, we also notice that the relief valve for the hydraulic flow will open at 50GPM, with a maximum of 6,000PSI. Crunching these numbers would suggest that the mulcher may be capable of running at near 175HP! (Of course, we always want to carefully respect the limits set out by the manufacturer to avoid injury and damage).

Blue Diamond's Swing Arm Stump Grinders

Of the three models of Swing Arm Stump Grinder attachments offered by Blue Diamond, all three require high-flow hydraulics.

The hydraulic flow rates on the swing arm stump grinder reflect the larger displacement hydraulic motors fitted on them. Depending on the swing arm stump grinder model, it will have a 130cc, 150cc, or 170cc hydraulic motor.

high flow stump grinder on a cat skid steer

While the large hydraulic motor is turning the stump grinders flywheel through a hard stump, there needs to be sufficient hydraulic flow remaining to operate four large hydraulic cylinders that control the swing arm.

The first two hydraulic cylinders are 2.5" by 6" and swing the stump grinder's "swing arm". The third cylinder measures 4.5" by 8" and lifts and lowers the swing arm. The last 2.5" by 12" cylinder extends the swing arm. Altogether, these cylinders require a large amount of hydraulic flow.

The smallest model of Swing Arm Stump Grinder that Blue Diamond offers is the 29-33 GPM model. It has a 60cc radial piston hydraulic motor, operates between 3,000 and 4,061PSI and is advertised as producing 55 to 77 Hydraulic Horsepower.

You can plug these numbers into our formula to double-check Blue Diamond's horsepower ratings. On the low end, with 29GPM and 3,000PSI, the stump grinder will have 51HP. On the high end, using 33GPM and 4,061PSI, the stump grinder will have 78HP.

Blue Diamond's Severe Duty Cold Planer

high flow cold planer on Kubota skid steer

Milling concrete and asphalt down to 8" and not having the cutting drum overcome with resistance takes a lot of horsepower. The severe-duty cold planer even uses a planetary gearbox to help produce more torque.

Blue Diamond's Severe Duty Cold Planer models require a 30 to 42GPM hydraulic flow rate with a 2,000 to 5,000PSI Pressure Range. As you know, this will give us 35 to 120 hydraulic horse power.

On top of this, the cold planer will have two hydraulic cylinders to set the depth of the cold planer and a hydraulic cylinder to control the planer's tilt.


Understanding flow and pressure isn't necessary to own and operate a skid steer, but it can help when choosing the right attachments for a job.

If you have further questions about high-flow skid steer attachments, you can contact me directly using the hyperlink provided.

Written by Cohen Meyer
Cohen Meyer is a product researcher and content contributor for Skid Steers Direct. Cohen has spent over 12,000 hours operating skid steers, telehandlers, excavators and tractors. He is a former business owner, certified welder and a self proclaimed tech geek.

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